Presently proposed heat sources for closed cycle engines, as for example used in torpedos, utilize a chemical reaction between lithium and sulfur hexafluoride to generate heat. The heat is applied to a working fluid, typically water, in a boiler which is vaporized therein. The resulting steam is fed to a turbine which provides for propulsion, condensed, and then returned via a pump to the boiler to be reused.
The sulfur hexafluoride is maintained in an oxidant tank and is injected at a controlled rate into a reaction chamber forming part of the boiler to react with lithium therein.
In the usual case, the lithium is in the form of a solid billet or the like and must be brought to a molten state for the reaction to proceed properly. This involves heating virtually the entire mass of the lithium and the boiler at least to the melting point of lithium (357.degree. F.).
Thus, in order to provide start-up of the system, a high intensity heat source must be used. One such system utilizes any of a variety of known start grains or squibs and pellets of aluminum potassium perchlorate.
Because of the temperature generated, local hot spots within the boiler can result in damage to the boiler wall or working fluid tubes.
A further problem is the fact that such systems are not inexpensive and the product of the chemical reaction between lithium and sulfur hexafluoride is a mixture of molten salts that, when cooled, results in a extremely hard, rock-like structure. Consequently, if the boiler is to be cleaned for reuse, there is required an extended period of deactivation by soaking the boiler in water to assure that all of the lithium has been oxidized. Moreover, the boiler must be tumbled in a long and laborious procedure to break up and remove the solidified products of the oxidation reaction.
Still another difficulty attends the use of such systems. The oxidant, sulfur hexafluoride, is typically stored as a liquid under normal temperature conditions. If the storage temperature is cold, the vapor pressure may fall below the pressure required to self expel the sulfur hexafluoride from the storage tank in sufficient quantities to maintain the reaction at the desired rate. At very low storage temperatures, the sulfur hexafluoride may even freeze.
Conversely, at high storage temperatures, the sulfur hexafluoride may be in a super critical state which, when system operation is initiated, causes it to expand to a mixture of liquid and vapor. Such a dual phase mixture can cause intermittant periods of very high flow to the reaction chamber in the boiler, disturbing the temperature control system customarily employed in such systems to the point that proper control cannot be maintained. Additionally, the sulfur hexafluoride injection nozzles by which the sulfur hexafluoride is injected into the reaction chamber, experience severe corrosion at the interface with the molten lithium which deleteriously affects their ability to be reused, probably due to thermal decomposition of the sulfur hexafluoride resulting in hot free fluorine which aggressively attacks the nozzles.
The present invention is directed to overcoming one or more of the above problems.
Other prior art of possible relevance includes U.S. Pat. No. 3,328,947 issued July 4, 1967 to Rose.